Bathroom waterproofing: what the rules require, and what to photograph

New Zealand's Building Code does not say “install a membrane”. Clause E3 Internal moisture requires the result: wall surfaces next to sanitary fixtures must be impervious and easily cleaned (E3.3.4), surfaces likely to be splashed must be impervious and easily cleaned (E3.3.5), and they must be constructed so water splash cannot penetrate behind linings or into concealed spaces (E3.3.6). A waterproof membrane under the tiles is how a tiled shower meets that.

The three clauses, in full

The determination puts the three together in one sentence: “the tiled walls to the shower must be impervious, easily cleaned, and be constructed in a way that prevents water splash from penetrating behind linings or into concealed spaces”. The objective behind them, clause E3.2(c), is to avoid the likelihood of damage to building elements caused by moisture.

What failure looks like

Determination 2024/054 is a useful thing to read precisely because it is so ordinary. Two tiled showers in a dwelling. A tiler's report identified damage to flooring and floor joists in the concealed space of the upper-floor framing, attributed to grouting failure along the tile joints of both showers. Photographs showed cracking to the grout. The same issue was in both.

The finding: “As the cracks allow water to enter the concealed space behind the shower walls, the tiled showers are not compliant with the relevant performance requirements of clauses E3.3.4, E3.3.5 or E3.3.6.” The formal decision records that the building work failed all three clauses. Nobody needed a consent for the work. It still failed.

Grout is not waterproofing

That is the practical lesson. Grout is a filler between tiles and it moves, cracks and wears. The membrane under the tiles is what stops water reaching the framing when the grout does crack. Re-grouting a shower that is leaking treats the symptom: it is worth doing when the grout is simply stained or tired, and worth nothing when water is already in the wall.

If you are deciding whether a refresh or a retile is the right scope, this is the question that decides it. A refresh keeps the membrane you have. A retile replaces it.

Nobody licenses waterproofers

Plumbing is licensed by the PGDB. Electrical work is licensed by the EWRB. Restricted building work needs an LBP. Applying a waterproof membrane in a domestic bathroom is not, on its own, any of those. There is no register to check.

So the questions worth asking a bathroom company are different: which membrane system are you using, are your applicators trained in that specific system, what is the substrate, how long between coats, and what do I get in writing afterwards. Membrane manufacturers publish installation instructions, and those instructions are the standard the installation is judged against.

What to photograph

1. The framing and substrate once the old linings are off, before anything new goes on.
2. Any rot, damp or damage found, before it is repaired, and again after.
3. The substrate sheets fixed and the joints and corners prepared.
4. The first membrane coat, wet, across the whole wet area including the floor and the upstands.
5. The final coat, cured, with the tin or pail in shot so the product is identifiable.
6. The shower tray or waste installed and sealed into the membrane.
7. The membrane product data sheet and the installation instructions, kept as files, not as a memory.

That set is the records pack we hand over at the end of a job, and it is the same set we would want as a buyer. What records to keep for exempt bathroom work covers where they go afterwards.